A polymeric hydrophobic substance is the most common type of conventional pressure-sensitive adhesive used to secure substrates to the human body. The majority of all adhesive bandages are made with this broad class of adhesive, which is used as a thin film. These polymeric hydrophobic substances are frequently produced by homopolymerization or copolymerizaton of one or more vinyl type monomers, especially acrylic esters, methacrylic esters, vinyl alcohol esters and vinyl ethers. Natural rubber and gum have also found use in conventional adhesive formulae.
When these prior art thin film, hydrophobic, polymeric, pressure-sensitive adhesives are used to secure a device such as an EKG monitoring electrode or to secure a bandage, removal frequently causes trauma, discomfort and soreness to the skin to which the adhesive was adhered. Skin trauma of this type may take the form of pulled hair, bruises, erythema, edema, blistering, removal of some epidermis, or tearing of the skin. The severity of the discomfort and trauma appears to be greater when the adhesive is allowed to contact the skin for an extended time. Frequently, EKG monitoring electrodes and postsurgical bandages are left of a patient's skin for up to a week and sometimes longer. Thus, the removal of these bandages and electrodes, quite often, is very painful, and soreness persists for some time.
Hydrophilic polymeric pressure-sensitive adhesives are also known in the prior art. Adhesives of this type are much less common than hydrophobic pressure-sensitive adhesives. Major uses of hydrophilic pressure-sensitive adhesives include use as an ostomy adhesive and as a conductive adhesive for securing an electrode to the human body. These pressure-sensitive adhesives are much less likely to cause skin trauma than the hydrophobic-type adhesives.
Some hydrophilic-type adhesives are made by chemically cross-linking a polymeric material to form the adhesive. Illustrative of this type of prior art are U.S. Pat. No. 3,998,215 to Anderson et al, U.S. Pat. No. 4,125,110 to Hymes, British Patent Application No. 2,034,184 of Hymes, U.S. Pat. No. 4,066,078 to Berg, and U.S. Pat. No. 4,094,822 to Kater. The adhesive of each of these documents is used in a patent electrode, and is conductive per se or provided with conductivity by, for example, using the adhesive to bond strands of a conductive material. In the Anderson et al, Hymes and Kater documents, it is stated that the adhesive is formed from an aqueous solution of the polymeric material.
In the Anderson et al patent, a porous webbed material is dipped into an aqueous solution of a hydro-gel former, for example, polyvinyl alcohol, to wet the webbed material, excess solution is scraped off, and the webbed material is then dipped into a solution of a gel-forming agent or a cross-linker for the hydrogel former, in order to form a hydrogel throughout the webbed material. The hydrogel is said to be lightly adherent to the body surface but sufficiently cohesive so that no residue remains upon removal thereof.
The Hymes patent relates to an electrode having an electrically conductive adhesive that contains a hydrophilic polysaccharide material (karaya), a hydric alcohol (glycerin) to provide plasticity, an electrolytic salt and propylene glycol. An alternate embodiment of this adhesive includes additive materials for cross-linking the hydrophilic polysaccharide material. These chemical cross-linking agents are said to include, for example, gelatin, polyvinyl acetate, certain polyesters and calcium salts.
The British patent application in the name of Hymes is similar to the U.S. patent to Hymes. The adhesive of this document is formed from dry karaya gum powder and a non-volatile liquid carrying either an ionizable salt or finely powdered silver or aluminum. In an alternate embodiment, the adhesive is comprised of 15-70% aqueous polyacrylic acid (25% concentration), 15-45% karaya, 10-35% water, 0-35% isopropyl alcohol, and 1-3% electrolyte. Additive materials for chemically cross-linking the karaya are said to include polymers such as vinyl acetate-ethylene copolymers and polyacrylic acid. At page 7, lines 48-50, it is mentioned that the substrate compound can be subjected to radiation to inhibit microbial growth, and that such radiation should be below 2.5 megarads gamma radiation.
The Kater patent pertains to an electrode having an adhesive-electrolyte material. Polyvinyl alcohol adhesives are said to be preferred, and a formulation is provided for an adhesive of this type, in which there is present 15-25% polyvinyl alcohol having a degree of polymerization equal to 1700 and being 88% hydrolyzed, and 5-10% glycerol. Suitably, the adhesive-electrolyte material is based upon polyvinylpyrrolidone (PVP), polyacrylamide or polyvinylpyridines.
The Berg patent, mentioned above, is concerned with an electrode having an electrically conductive, hydrophilic adhesive that is a chemically cross-linked hydrophilic interpolymer composition. The starting materials for preparing this interpolymer composition may be (a) an ester of an .alpha.,.beta.-olefinically unsaturated carboxylic acid and a monohydric or polyhydric alcohol having a terminal quaternary ammonium group, and (b) an .alpha.,.beta.-olefinically unsaturated comonomer.
Other documents relating to an adhesive for use in a patent electrode include British Patent Application No. 2,045,088 in the name of Larimore, U.S. Pat. No. 4,237,886 to Sakurada et al, U.S. Pat. No. 4,243,051 to Wittemann, U.S. Pat. No. 4,243,052 to Bailey, U.S. Pat. No. 4,248,247 to Ware et al, U.S. Pat. No. 4,267,840 to Lazar et al, U.S. Pat. No. 3,547,105 to Paine, U.S. Pat. No. 3,565,059 to Hauser et al, U.S. Pat. No. 3,607,788 to Adolph et al, U.S. Pat. No. 3,911,906 to Reinhold, Jr., U.S. Pat. No. 3,993,049 to Kater, U.S. Pat. No. 4,008,721 to Burton, U.S. Pat. No. 4,016,869 to Reichenberger, U.S. Pat. No. 4,067,342 to Burton, U.S. Pat. No. 4,112,941 to Larimore, U.S. Pat. No. 4,141,366 to Cross, Jr. et al, U.S. Pat. No. Re.24,906 to Ulrich, U.S. Pat. No. 3,845,757 to Weyer and U.S. Pat. No. 3,265,638 to Goodman et al. The Larimore British patent application and the Sakurada et al, Wittemann, Bailey, Ware et al and Lazar et al patents appear to be concerned with adhesives based upon cross-linked polymers. The patents to Reinhold, Jr., Larimore, Burton and Cross, Jr. et al pertain to an adhesive material based upon an acrylic polymer. Of these patents, the patent to Reinhold, Jr., has electrically conductive particles dispersed throughout the adhesive material thereof. An adhesive layer of this type can create non-uniform electrical transmisson, provide lower conductivity, require a high cost for manufacture, be difficult to manufacture, have lower adhesivity, and be unable to absorb perspiration, with there being a tendency to lose adhesion if only a slight amount of moisture is present. The Kater patent discloses that the adhesive thereof is suitably PVP-based. The Goodman et al patent is concerned with an electrolyte composition comprising an aqueous solution of sodium chloride that is preferably completely saturated with silver chloride and that contains up to 7.5% polyvinyl alcohol as a thickening agent. It is said that borax may be used to aid the polyvinyl alcohol in its thickening action.
Other patents pertaining to chemically cross-linking an aqueous solution of a polymeric material include U.S. Pat. No. 3,087,920 to Suzumura et al, U.S. Pat. No. 4,036,808 to Rembaum et al, U.S. Pat. No. 3,932,311 to Caldwell et al, U.S. Pat. No. 2,616,818 to Azorlosa, U.S. Pat. No. 4,089,832 to Yamauchi et al, U.S. Pat. No. 3,220,960 to Wichterle, U.S. Pat. No. 3,545,230 to Morse, U.S. Pat. No. 3,336,129 to Herrett et al, and U.S. Pat. No. 2,838,421 to Sohl. The Suzumura et al patent is concerned with a cold water-soluble polyvinyl alcohol that includes an admixture of partially saponified polyvinyl alcohol having a hydrolysis of 75-90%, a diaminostilbene optical bleaching agent, and a surfactant. At column 3, lines 33-35, of this patent, it is stated that in water, the partially saponified polyvinyl alcohol reacts with the diaminostilbene to form a three-dimensional bridge, thereby assuming a gel form, and at column 3, line 47, the cold water-soluble polyvinyl alcohol is stated to be useful as an adhesive.
The Rembaum et al patent relates to a conductive hydrogel formed by reacting the cationic polyelectrolyte thereof with a gel-forming polymer such as polyvinyl alcohol, polyacrylic acid or a polyether. At column 8, lines 19-22, it is explained that a cross-linked hydrogel can be prepared from aqueous solutions of a mixture of polyvinyl alcohol and polyacrylic acid or polyhydroxyethylmethacrylate. The gels of this patent appear to be adhesive.
The Caldwell et al patent is concerned with an electrically conducting adhesive composition containing a cross-linked acrylate and/or methacrylate polymer and silver particles. The Azorlosa patent relates to a process for preparing a coated paper in which polyacrylamide or a copolymer of acrylamide and acrylic acid is used as an adhesive. In a preferred embodiment, the coated paper is treated with a cross-linking agent so as to render the adhesive highly insoluble and strongly adhesive.
The Yamauchi et al patent pertains to a water-containing plastic composition that cntains a water-containing powdery gel obtained by subjecting a water-soluble polymer such as polyvinyl alcohol, polyacrylamide or PVP to a cross-linking reaction and then pulverizing the cross-linked product. Ionizing radiation can be used to effect the cross-linking. The plastic composition is suitable for manufacturing poorly combustible molding materials.
The Wichterle patent is concerned with a hydrogel essentially consisting of a cross-linked hydrophilic polymer and 20-97% of an aqueous liquid. The hydrogel can be made, cut, or otherwise shaped to produce, for example, a lens, a pessary, or a dialyzer diaphragm. Medicinally active agents such as antibiotics may be dissolved in the aqueous constituent to provide medication over an extended period.
The Morse patent relates to a flexible cooling device comprised of a reinforced layer of an insoluble hydrophilic gel. If desired, the gel can include materials to control the physical and chemical properties such as freezing point and chemical stability. Exemplary starting materials for preparing the gel include poly(ethylene oxide), PVP, polyacrylamide, polyvinyl alcohol, maleic anhydride-vinyl ether copolymers, polyacrylic acid, ethylene-maleic anhydride copolymers, polyvinyl ether, polyethyleneimine, polyvinyl alkyl pyridinium halides, and polymethacrylic acid. Insolubilization can be effected by ionizing radiation or chemical cross-linking. The gel must be capable of retaining relatively large quantities of a liquid. Water can be employed as the sole liquid, other liquids such as alcohols can be used, or mixtures of water and other liquids or solutes can be employed. When it is desirable to use more than one gel layer, a thin film of an inert material such as polyethylene or a metal foil is used to separate the gel layers and thereby effectively prevent adhesion of the layers when stacked.
The Herrett et al patent pertains to a plant growth medium containing an active agent and a water-insoluble, cross-linked polymeric material that serves as a matrix for the active agent. The polymeric material is illustratively polyvinyl alcohol, PVP, polyacrylic acid, polyvinyl acetate, polyacrylamide, and a copolymer of vinyl alcohol and vinyl acetate. The polymeric material is cross-linked either chemically or by ionizing radiation. Irradiation is carried out in the solid phase or in solution using water, for example, as the solvent. In one embodiment, a homogeneous water solution of the polymeric material is prepared and then irradiated for a period of time sufficient to cause the formation of a gel-like material, and the gel-like material is dewatered. Exemplary active agents are quaternary ammonium salts, copper sulfate, antibiotics and propylene glycol insect repellants. At column 10, lines 39-44, it is said that the roots of plants grown in soil formulations containing the cross-linked poly(ethylene oxide) of Herrett et al had adhered thereto particles of the polymeric matrix.
The Sohl patent is concerned with an adhesive tape having a water-soluble adhesive composition that is essentially a blend of a solid water-soluble polyvinyl carboxylic acid such as polyacrylic acid, and a compatible hydroxy-polyalkylene permanent elasticizer such as polyethylene glycol or polypropylene glycol. Another exemplary polyvinyl carboxylic acid is a 50/50 copolymer of polyvinyl methyl ether and maleic anhydride. Internal strength of the adhesive is increased by including in the adhesive mixture a chemical cross-linking agent. The cured type of adhesive is said to be more resistant to water but to dissolve in water when mechanically agitated or mixed.
Other prior art patents that in addition to the Morse and Herrett patents discussed above, pertain to a hydrogel based upon N-vinyl-2-pyrrolidone include U.S. Pat. No. 3,878,175 to Steckler, U.S. Pat. No. 3,759,880 to Hoffmann et al and U.S. Pat. No. 4,226,247 to Hauser et al. The Steckler patent is concerned with a highly spongy polymeric material characterized by swelling in water and being soft when wet. This spongy polymer is prepared by simultaneously copolymerizing and partially cross-linking 30-90 weight percent of an N-vinyl lactam monomer and 10-70 weight percent of an acrylate monomer. The spongy material is said to be adaptable for industrial applications, human use in toiletry, and as a sterile surgical dressing for sponging, wiping, or absorbing pus, blood and other body fluids during surgical operations. The Hoffman et al patent relates to the manufacture of insoluble and only slightly swellable poly-N-vinylpyrrolidone-2. The polymeric material of this patent is said to be a valuable absorbant for many purposes, especially as a beverage clarifying agent. The Hauser et al patent relates to an electrode having an adhesive that is preferably PVP-based. The adhesive is compounded by mixing with an active agent such as PVP, a plasticizer such as dioctyl phthalate, camphor or glycerin, and, alternatively, a conventional tackifier.
The Herrett et al, Yamauchi et al and Morse patents, discussed above, describe the use of radiation to cross-link a polymeric material. Similarly, U.S. Pat. No. 3,897,295 to Dowbenko, U.S. Pat. No. 3,264,202 to King, U.S. Pat. No. 2,964,455 to Graham, U.S. Pat. No. 3,841,985 to O'Driscoll et al, and U.S. Pat. No. 4,115,339 to Restaino pertain to the irradiation to polymeric materials.
In the Dowbenko et al patent, a solventless or nearly solventless solution of a polymer in a monomer is irradiated. The King patent pertains to forming a gel-like material by treating polymers of ethylene oxide with radiation. The gel-like material of this patent is said to have utility as a humidifier.
The O'Driscoll et al patent is concerned with irradiation of a solid, dry material containing PVP, and the Graham patent relates to the use of irradiation to modify solid articles made from polymeric alkylene oxides and polyvinyl ethers. At column 3, line 59-61 of the Graham patent, it is disclosed that a benzene-soluble polytetramethylene oxide was soaked in water prior to irradiation. In the Restaino patent, an aqueous solution of a water-soluble vinyl monomer is irradiated for the purpose of forming high molecular weight water-soluble polymers.
I believe this prior art and the other prior art of which I am aware, fails to provide a novel water-insoluble, hydrophilic, elastomeric, pressure-sensitive adhesive that is transparent, ultra-conformable and a soft, but strong, rubber-like solid that will absorb moisture that cannot be squeezed out; that will transmit oxygen, moisture, and drugs or salts soluble in the adhesive; and that will serve as a barrier to bacteria.
The adhesive could be useful as a coating on a supportive web-like substrate. The adhesive-coated web-like substrate could be used as a bandage, a burn or wound dressing, an ostomy device, a decubitus ulcer pad, a sanitary napkin, a diaper, a vibration or impact absorbing material such as a padding in shoes, splints, casts and orthopedic devices or an athletic padding, a sound absorbing material, or a medium for delivering a pharmacologically active agent. Additionally, a self-supporting layer of this adhesive could serve these same uses, and furthermore be useful as a cosmetic face mask and to secure a prosthesis or article of apparel to a mammalian body. One type of the novel adhesive could be electroconductive and function to attach an electrically conductive member of an electrode to a selected surface such as mammalian tissue.